Switch



J. F. VAN MEURS ETAL 2,611,062

SWITCH Filed April 29, 1949 INVENTORS. JOJMNIPIDHZZK IQNMEUBS. fijfimns VIWLMA AGEVI Sept. 16, 1952 fiatenfed Sept. 16, 1952 Eindhove'n, Netherlands, assignors to Hartford National Bank and Trust Company, Hartford,

Conn., as trustee Application April 29, 1949, Serial No. 90,436 In. the Netherlands May 22, 1948 Y '7 Claims. (omen-166) The invention relates to switches, more particularly selectors for automatic telephone systems.

' One of the principal problems with such switches is, in general, establishment of a reliableconta'ct with low'contact resistance. This may beachi'eved by increasing the contact pressure to a great degree but such a measure cannot be realised in practice with small, weakcurrent switchea-such as selectors, relays and the like. V g

Alternatively, the contacts may be coated with a layer of precious metalffor' example, gold. This method has a limitation in that particularly with contacts sliding over one another the layer of precious metal is soon worn through, unless it has a considerable thickness, which, however, is costly.

The object .of the invention is to mitigate these difiiculties.

According to the invention a switch, more particularly a selector for automatic telephone systems is characterized in that a piece of preciousme'taLy/hich itself need not act as an electric contact piece, is arranged on the switch in such manner that during. the switching movement this piece and one or more of the contact surfaces of the contact members rub over one another, so that a small amount of the precious metal is transferred to the contact surfaces.

Although, essentially, any precious metal may be used for the said purpose, gold and palladium are found to reduce the contact resistance at the contact surfaces to a greater extent than, for example, silver, although the latter metal is also serviceable under suitable conditions.

With a switch, a contact member of which co-operates with a series of countercontact members, the piece of precious metal may be arranged in the path of the contact piece of the first-mentioned contact member.

Such a switch is, for example, a rotary selector for automatic telephone systems, in which a rotary switching arm co-operates with a plurality of stationary contact members arranged in the arc of a circle. Here a piece of precious metal, for example, gold, may be secured to the contact bank so as to be wiped by the contact member of the rotary contact arm. After one or more switching operations the contact areas are thus coated with a thin layer of precious metal and the engagement of these contact areas with the contact surfaces of the stationary contacts results in a small amount of this metal being transferred to the latter so that the wiper loses part of the metal carried along therewith. The loss is compensated each time the wiper engages the stock piece. Even in the case of a small contact pressure a low contact resistance(' for example of a few milliohms) is thus ensured. This is particularly important with switches with which there is no electric voltage between the contacts or with which there is a small voltage which is too low to break through contaminatinglsubstances, if any, on the contact surfaces.

In order that the invention may be more clearly understood and readily carried into effect, it will now be described more fully with reference to the accompanying drawing, in which embodiments of switches according to the invention are shown. i V

Fig. I shows diagrammatically the system of contact members of a selector for automatic telephone exchanges. A row of flat, stripshaped contact pieces I is secured in the usual manner to an insulating strip 3. A wiper 5 of a switching arm. I, which is rotatable about a spindle S, is adapted to wipe the contact pieces i in succession. A piece of precious metal H, for example gold, which has approximately the same shape .as the contact pieces, is arranged at the beginning of the row of contact piecesl. During each rotation, the brush 5 wipes the piece of precious metal II, a small amount of precious metal being left on the contact areas. Part of it is transferred to the contact surfaces of the contact pieces I but only at th areas of engagement. The precious metal is therefore used as economically as possible, the additional cost entailed thereby being small. The contacts are, if gold is used, as it were continuously and automatically gilded without entailing any further cost.

It is desirable for the piece of precious metal i I to be secured to the contact carrier 3 so as to be readily removed and replaced, use being made, for example, of screws 13. When the precious metal is worn down, it may readily be replaced by another piece.

In order to economise precious metal, the part Il may comprise a strip of base metal, to which on either side pieces of precious metal are se cured. The precious metal of the worn pieces may be recovered by chemical agency.

If the number of countercontact members in the row is too great to provide all of them with a sufficient quantity of precious metal, a piece of precious metal may be arranged in this row at two or more points. Even distribution of the precious metal among the contact pieces I is thus ensured.

As an alternative with switches of this kind the piece of precious metal may be secured to the contact member co-operating with the row, for example to the rotary switching arm, so that, during the switching movement,it wipes the contact surfaces of the countercontact members arranged in a row, and coats them with a thin layer of precious metal, part of which in turn is transferred to the contact areas of the switching arm;

This embodiment is shown in Fig. 2, in which part a switch similar to that shown in Fig. 1 is shown, viewed in a radial direction from the shaft 9, the pieces of precious metal H being secured to the wiper of the contact arm. The contact pieces I thus engage directly with the pieces of precious metal, so that metal is transferred to each of the contact pieces I. Changing the pieces of precious metal is, however, less easy than in the embodiment shown in Fig.1.

' "A further kind of switches having contact pieces which slide over one another is shown in Fig. 3, which shows part of a vibrator comprising a resilient tag 21 having a contact piece 23, said jtag being adapted to be set vibrating in the usual manner by a driving mechanism (not shown). Theptag 2| supports a contact spring 25 having a cfonta'ct piece 21, which, in the positionshown in full lines, engages with a countercontact piece "29: The open position of the switch just before orafter closure is shown in dotted lines.

Fitted. in the contact piece 29 is a piece of precious metal I I. During the closing movement this piece initially engages the lower part of the surface of contact piece 21. It then moves upwards along this surface until the position shown in full linesis reached, a small amount of precious metal being thus transferred to the whole of the contact surface. This is eifected during the part 'of the contact period in which the contact pressureis low;fundue wear of the precious metal is thus prevented. In the position shown in dotted lines, the contact pressure is higher but the piece of precious metal 3| substantially no longer engagesthe countercontact piece 21.

What we claim is:

' 1. A selector switch for automatic telephone systems, comprising a plurality of stationary switch contacts disposed in a predetermined path,

each stationary contact being constituted by a member formed of a non-precious metal; an arm movable along said path and carrying a contact to engage the several stationary contacts; and a piece of precious metal so disposed in the path of movement of the contact on the movable arm as to cause the movable contact to wipe the piece of precious metal before moving on to engage the row of stationary contacts whereby the movable contact will rub oil a small amount of the precious metal and transfer it to the surfaces of the stationary contacts.

2. Aswitch as claimed in claim 1, characterized in that the piece of precious metal is made of gold.

3. A switch as claimed in claim 1, characterized in that the piece of precious metal is made of palladium.

v l. A switch as claimed in claim 1, a contact member of which co-operates with a row of countercontact members, characterized in that the piece of precious metal is arranged in the path of the contact piece of the first-mentioned conf tact member and during the switching movement is wiped by this contact piece.

5. A switch as claimed in claim 4, characterized in that a piece of precious metal is arranged in the row of countercontact pieces at two or more points. i 1' I I j 6, A switch as claimed in claim 1, a contact member of which co-operates with a row of countercontact members, characterized in that a piece of precious metal is secured to the first-mentioned contact member and during the switching movement wipes the contact surfaces of the countercontact members.

v7. A switch as, claim 1, characterized in that the precious metal is arranged so as to be readily removed and replaced. f I JOHAN FREDERIK VAN MEURS.

ALBERTIUS VENEMA.

REFERENCES CITED The following references are of record in the file of this patenti a UNITED STATES PATENTS Larson Oct. 10, 1944 

